No, you don't have Full-time 4wd. Sometimes referred to on here as AWD.
When you push the "4WD" button, it shifts into Part-time 4HI 4wd, which should Ideally only be used on surfaces where wheel slip can occur.
Without the center differential in the T-case, which the 4Runners with AWD capability have, you can having binding in the driveline. If the binding becomes severe enough, you can break parts. However, usually the binding will just dramatically increase driveline wear, and parts won't fail completely.
. In an automotive sense, a differential allows two output shafts to turn at different speeds. A traditional part-time four wheel drive system does not have a differential between the front and rear driveshafts... when the truck is in four wheel drive, the driveshafts are both turning at the same speed, all the time. A "full time" four wheel drive system has a differential on the tcase functionally similiar to the differential on your front and rear axles which allows the front and rear shafts to differentiate. Some full time four wheel drive systems (like the multimode on 4Runners) have a "center diff lock", which locks the center differential and prevents the driveshafts from spinning at different speeds exactly the same way an elocker on an axle differential prevents the axle shafts from spinning at different speeds. Other full time four wheel drive systems don't have that ability to lock that center diff.
